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  Java Practices -> Iterate without an index
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<div class='page-title'>Iterate without an index</div>

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<br>Some programmers have a strong preference for using a 
<tt><a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/foreach.html">for-each</a></tt>
loop or an 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Iterator.html">Iterator</a></tt> 
instead of <tt>for</tt>-loops. 

<P>The traditional <tt>for</tt>-loop always uses a loop index - an integer that identifies each iteration of the loop.
Loop indexes have always been a fruitful source of error. For example, off-by-one errors are very common 
in programming, and they are often related to these loop indexes. In addition, the (rather unnatural)  
computer science tradition of starting loop indexes from <tt>0</tt> instead of from <tt>1</tt> is a
continual source of trivial errors.

<P>Since they are more error prone, <tt>for</tt>-loops should generally be avoided if there is an alternative.

<P><b>Example</b>
<br>
<PRE>

<span class='keyword'>import</span> java.util.*;

<span class='comment'>/** Different iteration styles. */</span>
<span class='keyword'>public</span> <span class='keyword'>class</span> IterateNoIndex {
   
  <span class='comment'>/** 
  * Iterating without an index is more compact and less 
  * error prone. 
  */</span>
   <span class='keyword'>public</span> <span class='keyword'>void</span> withoutIndex(){
     <span class='comment'>//for-each loop
</span>     List&lt;String&gt; trees = Arrays.asList(<span class='literal'>"Maple"</span>, <span class='literal'>"Birch"</span>, <span class='literal'>"Poplar"</span>);
     <span class='keyword'>for</span>(String tree: trees){
       log(tree);
     }
     
     <span class='comment'>//with an Iterator
</span>     Iterator&lt;String&gt; iter = trees.iterator();
     <span class='keyword'>while</span> (iter.hasNext()) {
       log(iter.next());
     }
   }
   
   <span class='comment'>/** Iterating with an index is more error prone. */</span>
   <span class='keyword'>public</span> <span class='keyword'>void</span> withIndex(){
     <span class='comment'>//traditional for-loop
</span>     <span class='keyword'>for</span>(<span class='keyword'>int</span> idx=<span class='literal'>0</span>; idx &lt; <span class='literal'>10</span>; ++idx){
       log(<span class='literal'>"Iteration..."</span>);
     }
   }
   
   <span class='comment'>// PRIVATE //
</span>   <span class='keyword'>private</span> <span class='keyword'>void</span> log(String aMessage){
     System.out.println(aMessage);
   }
}
 
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction852c-2.html?Id=125'>Two ways of using Iterator</a> <br>
 
  
  <a href='TopicAction23e0-2.html?Id=196'>Use for-each liberally</a> <br>
 
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